Method for determining vehicle velocity

ABSTRACT

A method and device for determining a vectorial vehicle velocity by estimating a mean value for the vehicle velocity by using a position-finding device to obtain a first value, and to then compare this first value with a second value estimated using inertial sensors.

FIELD OF THE INVENTION

[0001] The present invention is directed to a method and device fordetermining a vectorial vehicle velocity.

BACKGROUND INFORMATION

[0002] It is already discussed in the German patent application DE10049905 (not a prior publication) to employ a kinematic sensor platformin a control unit, where the kinematic sensor platform includes inertialsensors such as acceleration sensors and rotational speed sensors. Thatmakes it possible to determine a value for the vectorial vehiclevelocity. This value can be supplied to a vehicle dynamics controlsystem (ESP=electronic stability program), so that an ESP regulates thevehicle dynamics according to the sensor values. This related arttherefore leads to the object of improving the determination of thevectorial vehicle velocity.

SUMMARY OF THE INVENTION

[0003] An exemplary method of the present invention for determining avectorial vehicle velocity, has the advantage over the related art thatthe inertial sensors are augmented by the addition of a position-findingdevice which is used to determine a second value for the vectorialvehicle velocity, in order to produce, by comparing the value that wasdetermined using the inertial sensors and the value that was determinedusing the position-finding device, an average value that represents abetter estimate of the vectorial vehicle velocity. That also makes itpossible to dispense with selective under-braking to determine thevehicle velocity, so that such interventions by a regulator are nolonger necessary. This results then on the whole in a shortening of thestopping distance. An additional advantage is that the improvedvectorial vehicle velocity enables the control of vehicle dynamics byESP to be improved.

[0004] In an exemplary embodiment the position-finding device is a GPS(global positioning system) which makes possible a very precisedetermination of position and thus also a very precise determination ofvelocity. The velocity may be determined from the Doppler effect of thecarrier signals or from the carrier phases. A velocity vector istherefore available, because both the magnitude and the direction arethereby determinable as components of the velocity vector. This may beimproved by using two or three antennas, so that the orientation isdeterminable in two dimensions or in three dimensions.

[0005] Furthermore, a vehicle dynamics control system such as ESP isimproved thereby, since a maximum number of bits of sensor informationare made available to the ESP system. The weighting of the velocityvalues that have been determined using the position-finding device andthe inertial sensors depends on the number of satellites theposition-finding device, as a satellite-based system, is able to receiveat the time of measurement, the number of antennas used, and in the caseof the velocity determined by the inertial sensors, the number of tiresthat are slipping. Establishing a mean value then makes it possible toestimate the vectorial vehicle velocity as precisely as possible.

[0006] In another exemplary embodiment of the present invention, adevice for carrying out or performing the method according to thepresent invention is available, which has a sensor platform including aposition-finding device, with either two or three antennas beingemployed when a GPS system is used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 shows a schematic diagram of the method according to thepresent invention.

[0008]FIG. 2 shows a schematic diagram of a vehicle bus system.

[0009]FIG. 3 shows a schematic diagram of a kinematic sensor platformhaving a position-finding device.

DETAILED DESCRIPTION

[0010] For some time the suppliers of vehicle manufacturers have beenworking intensely on vehicle systems that are intended to stabilize thevehicle states in situations of borderline vehicle dynamics. ABS(anti-lock brake system), TCS (traction control system or ASR (anti-slipregulation)) and ESP are employed. The sensor technology on which suchsystems rely includes primarily yaw rate sensors, transverseacceleration sensors, and sensors of wheel rotation speed, brakepressure and steering angle. These sensors make it possible to determinethe driver's intention in regard to direction and acceleration/braking,and on this basis the motion state of the vehicle is determined.Essential variables for correctly regulating the state of the vehicleare the vehicle velocity, the yaw rate and the float angle of thevehicle.

[0011] Control units are now able to have an intelligent sensorplatform, where such a sensor platform represents an integration ofinertial sensors, i.e., linear acceleration sensors and yaw ratesensors. Now the objective is to estimate the driving condition with thesupport of a model.

[0012] According to an exemplary embodiment of the present invention, anintelligent sensor platform of this sort is now augmented by theaddition of a position-finding device that is designed to enable animproved estimation of the vectorial vehicle velocity. This improves theeffect of a vehicle dynamics control system such as ESP.

[0013]FIG. 2 shows a schematic block diagram illustrating how varioussystems are connected with each other in a vehicle via a bus. A vehiclebus 19, for example a CAN bus, here connects a control unit that is madeup in part of a bus controller 18, a processor 17 and a sensor platform16 to a headlight beam adjustment device 28 and an ESP system 30. Bothheadlight beam adjustment device 28 and ESP system 30 have buscontrollers 27 and 29 respectively, to enable communication via bus 19.Sensor platform 16 is connected, via a data input, to processor 17,which processes the sensor data and then conveys appropriate data suchas an estimate of vehicle velocity via bus controller 18 to headlightbeam adjustment device 28 and vehicle dynamics control system 30.

[0014]FIG. 3 shows the layout of sensor platform 16, which is connectedto processor 17. There are three GPS receivers on sensor platform 16.The first GPS receiver has an antenna 20 and a receiving device 21 whichis connected to a first data input of processor 17. A second GPSreceiver, made up of an antenna 22 and a GPS receiving device 23downline, is connected to a second data input of processor 17. A thirdGPS receiver, made up of an antenna 25 and a GPS receiving device 24, isconnected to a third data input of processor 17. A group of inertialsensors 26 followed by measurement amplification and digitization areconnected to a fourth data input of processor 17. GPS receiving devices21, 23 and 24 are connected to each other by leads, in order tosynchronize them with each other.

[0015] In an alternative embodiment, only two GPS receivers may be usedinstead of three. This makes it possible to determine the orientation intwo dimensions, whereas three antennas enable determination of theorientation in three dimensions. Also, antennas 20, 22 and 25 may beconnected to a receiving device that is able to interpret the differentsignals together. In that case the signals from antennas 20, 22 and 25are queried one after the other by the single receiving device.Processor 17 then determines a different value for the vectorialvelocity in each case from the GPS data and the sensor data. Bycomparing these two values an average or mean value is then determined,in order to determine the best possible estimate of the vectorialvehicle velocity. This value is then transmitted to vehicle dynamicscontrol system 30. From the vectorial vehicle velocity the float anglemay be determined, which is used for headlight leveling device 28.

[0016] The schematic diagram shown in FIG. 1 describes the methodaccording to the present invention. In block 1, ESP sensors (inertialsensors 26) sense linear acceleration and yaw rate values that occur inthe vehicle. An ESP estimator 2 uses these values to determine a firstvalue for velocity 3 and a corresponding weighting 4 for this velocityvalue. Velocity 3 is determined from the accelerations that occur, i.e.,primarily by integration of the determined acceleration values.Weighting 4 is determined from properties of the vehicle such as theslip values of the tires. Velocity value 3 is then multiplied in block 5by weighting 4. GPS sensors 6 determine the exact position of thevehicle for each point in time, as shown in FIG. 3. Thus, over time thevectorial velocity may be determined. A downstream GPS electronicssystem 7, which is integrated into processor 17 in FIG. 3, uses thisvalue to determine a second velocity value 9 and a weighting 8 for thissecond velocity value. In a multiplier 10, velocity value 9 is thusmultiplied by weighting 8. In block 11 weighting values 4 and 8 areadded together. In block 12 the weighted velocity values are added, andthis added value is then divided in block 13 by the sum of theweightings from block 11, in order to determine an average value inblock 14. This average value is then transmitted via bus 19 to a vehicledynamics control system 15, in this case the ESP. As an additionalvalue, weighting 8 is transmitted to vehicle dynamics control system 15.The weightings provide information about the quality of the measuredvalues. If the GPS supplies very reliable information about a vehiclevelocity, for example, the corresponding weighting is very high.

[0017] A weighted mean value is thus available for the velocity estimatein regard to magnitude and direction, i.e., vectorially.

[0018] Now if velocity value 9 is present with suitably good quality, asdetermined by vehicle dynamics control system 15, it is not necessary toactively under-brake one wheel by ESP regulator 15 in order to determinethe vehicle velocity.

[0019] A significant difficulty is that the vehicle velocity iscalculated using GPS in an environmentally fixed coordinate system. Inthe ESP system, in contrast, the velocity values are present in avehicle-fixed coordinate system. The vehicle velocities are identifiedbelow in the lateral, transverse, and vertical directions with VX, VY,and VZ.

[0020] A transformation may be made between the two systems, i.e.,between the environmentally fixed and the vehicle-fixed coordinatesystems, if the orientation of the vehicle in the environmentally fixedsystem is known. If two GPS antennas are positioned along thelongitudinal axis of the vehicle, the position of the correspondingconnecting line {right arrow over (a)} in the plane may be determined.The vector {right arrow over (a)} is determined in environmentally fixedcoordinates. This line is rigidly connected to the vehicle and istherefore used as reference line for the coordinate transformation. Thisis done by creating the projection of the 3-D velocity vector {rightarrow over (V)}, onto connecting vector {right arrow over (a)} wherebythe velocity V_(x) along the longitudinal axis of the vehicle isobtained:

V _(x) ={right arrow over (V)}{right arrow over (α)}/|α|.

[0021] The velocity

V _(transv) ={right arrow over (V)}−v _(x){right arrow over (α)}/|α|

[0022] in any case is perpendicular to the longitudinal axis of thevehicle. When working with two GPS antennas, the information about theposition of the vehicle about the vehicle longitudinal axis, i.e., theroll angle, is lacking. This missing information may be supplied whenthere are three GPS antennas present. In this case the velocity in V_(y)and V_(z) may be determined. With only two antennas along the vehiclelongitudinal axis, an assumption must be made in order to be able tocalculate V_(y). This assumption is that the roadway does not slope toan edge, i.e., that it has no slope. Consequently V_(y) is obtained fromV_(transv) by setting the z component equal to zero.

[0023] Float angle α is a very important variable for the vehicledynamics, but unfortunately it may only be measurable with greatdifficulty. It is defined by the equation tan(α)=Y_(y)/V_(x). Since bothvelocities in this equation are now known, the float angle may bedetermined. In accordance with the figures which describes the methodfor calculating the vehicle velocity, in addition to the velocity, thefloat angle calculated by the sensor platform is determined using boththe ESP sensor system and the GPS sensor system.

1-8. (canceled)
 9. A method for determining a vectorial vehiclevelocity, the method comprising: determining a first value of thevectorial vehicle velocity using at least one inertial sensor;determining a second value of the vectorial vehicle velocity using atleast one position-finding device; and determining a third value of thevectorial vehicle velocity based on a comparison of the first and secondvalues of the vectorial vehicle velocity.
 10. The method of claim 9,wherein the at least one position-finding device uses a satellite-basedpositioning system to determine the second value.
 11. The method ofclaim 10, wherein the satellite-based positioning system includes a GPSSystem.
 12. The method of claim 9, further comprising: supplying thethird value to a vehicle dynamics control system.
 13. The method ofclaim 9, further comprising: supplying the third value to a headlightleveling device.
 14. The method of claim 9, wherein the third value isdetermined by weighting the first and second values and determiningtheir average, the average being the third value.
 15. A device fordetermining a vectorial vehicle velocity, comprising: at least oneinertial sensor; at least one position-finding device; and a processoroperable to perform the following: receiving a first value from the atleast one inertial sensor, receiving a second value from the at leastone position-finding device, and computing a third value based on acomparison of the first and second values; wherein the device isconnectable to at least one of a vehicle dynamics control system and aheadlight leveling device.
 16. The device of claim 15, wherein the atleast one inertial sensor and the at least one position-finding deviceare located on a common sensor platform.
 17. The device of claim 15,wherein the at least one position-finding device includes two antennasto receive signals that are relevant for a position-finding.
 18. Thedevice of claim 15, wherein the at least one position-finding deviceincludes three antennas to receive signals that are relevant for aposition-finding.